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A STUDY  IN  CONDUCTIVITY  MEASUREMENTS 

BY 

VIRGIL  RICHARD  SULLIVAN 

AND 

JOHN  WILLIAM  APPLING 


THESIS 


FOR  THE 


DEGREE  OF  BACHELOR  OF  SCIENCE 
IN 

CHEMISTRY 

COLLEGE  OF  LIBERAL  ARTS  AND  SCIENCES 

UNIVERSITY  OF  ILLINOIS 


1921 


Digitized  by  the  Internet  Archive 
in  2015 


https://archive.org/details/studyinconductivOOsull 


TABLE  OF  CONTENTS. 

I.  General  Introduction,  p.l. 

II.  Regulation  of  the  Thermostat,  p.l. 

III.  Booth  circuits  and  the  Calibration  of  the  Kohlrausch  Bridge. 
pp.1-4,  Diagram  of  Bridge  and  Commutator  p.3. 

IV.  Reconstruction  of  the  Water  Purifying  Quartz  Still,  pp.4-5. 

V.  Apparatus  for  Steaming  out  the  Cell  and  Electrodes,  p.5. 

VI.  Determination  of  the  Cell  Constant  of  the  Quartz  Cell,  pp.5-6. 

VII.  Attempts  at  the  Preparation  of  ultra  Pure  Conductivity  Water. 

p.6. 

VIII.  Bibliography,  p.7. 

IX.  Acknowledgment,  p.7. 


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I.  GENERAL  INTRODUCTION. 


In  undertaking  this  problem,  the  authors  had  in  mind  a contin- 
uation of  some  work  carried  out  previously  in  this  laboratory  by 
H.J.Weiland,  in  which  some  very  careful  measurements  were  made  of 
the  conductivity  of  dilute  solutions  of  potassium  chloride,  the  in- 
tention in  this  case  being  to  study  dilute  solutions  of  hydrogen 
chloride.  For  further  information  concerning  the  bridges  used,  the 
preparation  of  conductivity  water  and  the  prevention  of  contamina- 
tion of  it  by  the  air,  etc.  reference  is  made  to  this  thesis. 

II.  REGULATION  OF  THE  THERMOSTAT . 

No  conductivity  work  having  been  done  here  for  some  time,  the 
apparatus  as  used  by  We  Hand  was  found  to  be  sadly  in  need  of  re- 
pair or  replacement.  Attention  was  first  directed  to  the  oil  ther- 
mostat, using  the  ordinary  mercury  regulator  and  electric  circuits 
with  the  relay.  Some  trouble  was  experienced  in  aa justing  the  ap- 
paratus so  that  the  bath  would  maintain  a sufficiently  constant 
temperature  over  long  intervals  of  time.  Instead  of  using  a plati- 
num wire  to  make  contact  with  the  mercury,  a sharp  pointed  iron 
rod  was  finally  substituted.  The  point  was  carefully  blued,  and 
after  being  used  for  some  time  appeared  to  be  unaltered.  This  eas- 
ily furnished  for  several  hours  at  a time  a very  close  temperature 
regulation  ( + 0.005°).  After  this  the  thermostat  gave  no  trouble. 

A cooling  coil,  stirring  apparatus,  etc.  exactly  like  that  used  by 
Weiland,  was  used.  Special  mention  should  be  made  at  this  point  of 
the  satisfactory  use  of  a device  reported  by  King  (2)  to  protect 
the  mercury  contact  in  the  regulator  from  oxidation. 

III.  BOOTH  CIRCUITS  AND  THE  CALIBRATION  OF  THE  KOHLRAUSCH  BRIDGE. 

The  circuits  in  the  sound  proof  booth  and  those  of  the  high 


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frequency  generator  having  been  disarranged,  some  tracing  of  cir- 
cuits and  re— wiring  was  found  necessary.  It  was  necessary  to  re- 
wind the  drum  of  the  Kohlrausch  bridge,  and  to  re-calibrate  it,  the 
data  for  which  is  given  below: 

For  R~  a resistance  box  was  inserted  and  direct  current  was 
used  from  two  dry  cells  across  the  ends  of  the  bridge, 


Rc 

= 5Q 

30 

70 

20 

10 

R 

= 700 

700 

700 

700 

700 

a 

= 69S.3 

429.8 

957.5 

289.8 

146.0 

Si 

(Calc.)  - 9489.5 

9458.4 

9532.5 

9432.8 

9366.0 

’• 

Equation  used 

R _ b 4- 

En  Average  value 

9455.8 

R a 

a. 

Rc 

= 700 

210 

700 

700 

700 

R 

= 10 

10 

35 

40 

55 

a 

- 849.8 

516.5 

495.0 

428.0 

231.0 

TP 

(Calc.)  =9664.2 

9637.0 

9605.0 

9582.0 

9556.0 

Equation  used  R _ b Average  value  9608.8 

Rq  a _i£- 

This  gives  a total  length  for  the  bridge  of  just  about  20,064 

parts  ( i.e.,  units  of  length). 

The  following  method  of  evaluating  the  total  length  of  the 

bridge  wire  checked  very  well  with  the  one  just  given: 

The  resistance  of  the  wire  on  the  drum  was  measured,  and  found 

to  be  12.52  ohms,  the  length  of  the  wire  being  arbitrarily  taken  as 

1003  units.  The  total  resistance  of  the  bridge,  including  extension 

coils,  was  250.36  ohms,  hence  250.36  x 1003  - 20,055'  parts,  being 

12.52 

apparent  length  of  the  bridge  wire.  For  final  values,  the  total 

length  of  the  bridge  was  taken  as  20,060  parts,  divided  as  follows: 

( Continued  on  Page  4.) 


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page,  R is  a standard  resistance  box,  R is  the  cell,  En  and  E are 
the  extension  coils  to  the  Kohlrausch  bridge  (arms  represented  by 
a and  b) , T is  the  telephone,  G is  the  ground,  N represents  the 
leads  to  the  high  frequency  generator,  a'  and  b'  are  the  two  arms 
of  the  constant  ratio  bridge,  and  TV  is  the  second  lead  to  the 
telephone  when  the  constant  ratio  bridge  is  in  use. 


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- 9454,  Er  - 9606,  on  toe  arum  = 1000.  This  calibration  must 
be  taken  only  as  approximate,  and.  not  final.  It  answered  very  well 
in  the  preliminary  work.  For  the  final  measurements  the  intention 
was  to  use  the  apparatus  as  a "commutating  bridge"  and  thus  obviate 
the  necessity  for  any  very  extensive  calibration.  The  following 
simple  scheme  was  devised  for  the  convenient  interchanging  of  the 
Kohlrausch  bridge  and  tiie  constant  ratio  bridge  ( see  the  diagram 
on  the  preceding  page):  R-  and  are  connected  to  the  known  re- 

sistance R,  T^_  is  one  lead  to  the  telephone,  the  other  being  at- 
tached to  the  middle  of  the  drum  of  the  Kohlrausch  bridge  and  to 
the  proper  place  on  the  constant  ratio  bridge,  B-^  and  are  con- 
nected to  the  ends  of  the  Kohlrausch  bridge,  R-  and  0^  are  con- 
nected to  the  ends  of  the  constant  ratio  bridge,  and  R^  and  Gj_  are 
connected  to  the  high  frequency  current.  It  can  be  seen  that  by 
interchanging  of  the  cup  connectors  on  the  commutator,  either 
bridge  may  be  thrown  into  the  circuit  separately. 

IV.  RECONSTRUCTION  OF  THE  WATER  PURIFYING  QUARTZ  STILL. 

The  repair  of  the  quartz  still  for  the  final  purification  of 
the  water  presented  the  greatest  difficulties,  and  even  at  the  last 
was  not  very  satisfactory  in  use.  The  two  nichrome  heating  units 
used  in  heating  the  quartz  flask  were  eitiier  badly  corroded  or  en- 
tirely burnt  out.  They  were  re-wound  and  embedded  in  a mixture  of 
asbestos,  silica,  and  bone  ash,  which  could  readily  be  worked  into 
any  desired  shape  when  wet.  Considerable  care  had  to  be  exercised 
in  drying  this  mixture  with  the  current  on,  for  the  wire  seemed  to 
"rot"  very  easily  and  crumble  to  pieces.  It  was  dried  very  slowly. 
Each  unit  had  a resistance  of  about  20.5  ohms  and  they  were  connec- 
ted to  the  110  volt  D.G.  line  in  series  with  an  ammeter  and  a rheo- 


. 


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f 


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stat.  Three  amperes  of  current  in  the  bottom  unit  was  sufficient 
to  keep  the  water  hot  while  air  passed  thru  the  still, while  with 
five  amperes,  the  water  distilled  over,  thus  rendering  the  use  of 
the  upper  heating  unit  optional. 

The  purifying  air  train  had  to  be  rebuilt,  and  was  modeled 
directly  after  the  one  used  by  Weiiand.  It  was  found  impossible  to 
make  the  air  compressor  w ork,  so  finally  recourse  was  had  to  the 
air  line  in  the  building.  Several  Drexel  bottles,  filled  with  con- 
centrated sulfuric  acid,  glass  wool,  sodium  hydroxide,  and  two 
filled  with  cotton,  were  inserted  in  the  air  line  before  the  train 
described  by  Weiiand.  It  was  thought  that  this  extra  precaution 
would  eliminate  moisture,  grease,  and  other  undesirable  constitu- 
ents, but  the  investigations  aid  not  reach  a point  giving  any  de- 
finite assurance  on  this  subject. 

V.  APPARATUS  FOR  STEAMING-  OUT  THE  CELL  AND  ELECTRODES. 

The  apparatus  for  steaming  out  the  electrodes  is  described  by 
Weiiand.  In  order  to  avoid  the  use  of  gas,  especially  when  it  was 
desirable  to  steam  out  the  apparatus  over  night,  an  electric  heat- 
ing unit  was  built,  and  mounted  in  a asbestos  wire-gauze.  Number 
18  ni chrome  wire  was  used,  enough  to  give  a resistance  of  about  28 
ohms,  and  the  coil  was  embedded  in  a mixture  of  asbestos,  silica, 
and  bone  asn,  so  arranged  to  hold  a three  liter  round  bottom  Pyrex 
flask.  Using  this  form  of  apparatus,  very  good  results  were  ob- 
tained, even  when  used  for  considerable  time. 

VI.  DETERMINATION  OF  THE  CELL  CONSTANT  OF  THE  QUARTZ  C^LL. 

In  order  that  the  later  work  on  the  preparation  of  conductiv- 
ity water  might  have  some  significance,  tentative  determinations  of 
the  cell  constant  of  the  quartz  cell  were  made,  using  an  approxi— 


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r 


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raately  N/lOOO  solution  of  potassium  chloride  with  cell  Number  16, 
whose  cell  constant  was  known*  No  attempts  were  made  to  determine 
this  value  with  any  degree  of  accuracy,  because  it  was  realized  the 
cell  would  have  to  be  repaired  before  actual  work  could  be  done 
with  it,  and  this  investigation  was  principally  concerned  with  pre- 
liminary work,  in  some  measure  to  prepare  for  later  work.  For  this 
reason,  it  does  not  seem  necessary  to  give  any  data  upon  these 
approximate  measurements. 

VII.  ATTI  AT  THE  PREPARATION  OF  ULTRA-PURE  CONDUCTIVITY  WATER. 

Knowing  Approximately  the  cell  constant  of  the  quartz  cell,  it 
was  thought  advisable  next  to  start  to  prepare  the  ultra-pure  con- 
ductivity water.  The  method  and  general  procedure  has  been  that 
outlined  by  Wei land.  The  first  run  was  begun  about  march  15,  1921 
and  subsequently  repeated  several  times.  No  encouraging  results  can 
be  reported  in  any  of  tnese  series  because  of  the  difficulties  ex- 
perienced in  working  with  the  apparatus.  The  general  conductivity 
still  gave  no  little  trouble  because  of  low  steam  pressure  and 
faulty  valves,  so  that  in  several  cases  the  purity  of  the  water 
started  with  was  questionable.  Again  the  rotary  air  compressor 
(which  was  being  used  at  that  time)  quit  working  with  considerable 
regularity,  and  when  the  stream  of  purified  air  could  not  be  forced 
thru  the  still,  the  experiment  was  useless.  In  addition,  the  quartz 
platinum  seal  of  the  quartz  cell  electrodes  had  broken  loose,  and 
attempts  at  repairing  proved  useless,  so  finally  worm  had  to  be 
suspended.  In  no  case,  in  so  far  as  it  was  possible  to  determine, 
was  conductivity  water  of  a purity  (specific  conductance)  better 
than  0.25  x 10  reciprocal  ohns  obtained. 

It  is  regretted  that  the  problem  had  to  be  abandoned  at  this 


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indefinite  stage,  and  it  is  hoped  that  it  can  be  completed  at  some 
future  time. 

VIII.  BIBLIOGRAPHY . 

(1)  Thesis,  University  of  Illinois,  1917,  H.J.Weiland. 

(2)  Journal  of  the  American  Chemical  Society,  October  1920,  p.2058. 

IX.  ACKNOWLEDGMENT . 

The  writers  desire  to  express  their  thanks  to  Dr . G-.Dietrichson 
under  whose  direction  the  investigation  was  carried  out.  They  also 
wish  to  thank  other  members  of  the  department  for  their  interest 
and  cooperation  during  the  past  year's  worK. 


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